Additive for lubricating composition

ABSTRACT

AN EP ADDITIVE PACKAGE FOR AVIATION ESTER LUBES COMPRISES A TRIARYL PHOSPHATE AND DIALKYLAMINE HYDROCARBYL PHOSPHATE, OPTIONALLY IN ADMIXTURE WITH DIHYDROCARBYL ALKYLAMINE PHOSPHATE.

United States Patent US. Cl. 25232.5 15 Claims ABSTRACT OF THE DISCLOSURE An EP additive package for aviation ester lubes comprises a triaryl phosphate and dialkylamine hydrocarbyl phosphate, optionally in admixture with dihydrocarbyl alkylamine phosphate.

The present invention relates to an additive for use in a lubricating composition.

Lubricating compositions are required to enable parts to move relative to each other with a minimum of friction. Generally speaking, the more viscous the lubricating composition at the operating temperature, the more easily it is able to maintain an apparent separation between the relatively moving parts when a load is applied which tends to force the two parts together. However, high viscosity lubricating compositions are subjected to a number of disadvantages compared with lower viscosity compositions of the same chemical type, among which is a greater tendency to decompose under the action of heat to non-volatile deposits, such as coke.

The problem is particularly acute when the parts to be lubricated are the bearings of the turbine spool of gas turbine engines, although the problem may be met in other connections.

One method of overcoming the problem is to employ a relatively low viscosity lubricating composition which is accordingly less prone to form non-volatile decomposition products at elevated temperatures. However, such compositions are generally less able to resist the loadings and thus prevent wear between the relatively moving parts, a property which is generally correlated with their kinematic viscosities, and it is advantageous to incorporate in such compositions additives which improve their load-bearing properties.

According to the invention, there is provided an additive for use in a lubricating composition comprising the combination of a component (a) which is a neutral (as hereinafter defined) hydrocarbyl phosphate with a component (b) which is a neutral alkylamine hydrocarbyl phosphate at least some of which is dialkylamine monohydrocarbyl phosphate.

By neutral phosphate is meant a derivative of phosphoric acid in which all three replaceable hydrogen atoms of each molecule of phosphoric acid have been replaced by the said substituents.

Each alkylamine group in component (b) may have from 8 to 18 carbon atoms, more preferably 10 to 14 carbon atoms, and the alkyl radical of at least one of the alkylamine groups may be a tertiary alkyl radical.

The hydrocarbyl group(s) of component (b) may be alkyl or aryl and have from 1 to- 9 carbon atoms. Preferably the hydrocarbyl group(s) are C -C aliphatic.

The hydrocarbyl groups of component (a) may be the same or different and either alkyl, aryl or aralkyl.

Preferably the proportion of component (a) will exceed the proportion of component (b) and the component r. we

(a) may form from 50 to 97.5 wt. percent of the additive preferably to 97.5 wt. percent.

In addition to the foregoing components (a) and (b) the additive may also comprise a metal deactivator to mitigate corrosion of metal that the additive contacts when in use in a lubricating composition, an oxidation inhibitor to inhibit oxidation of the lubricating composition, and an anti-foaming agent.

The additive of the invention is found to impart a surprising improvement to the load carrying properties of lubricants, and hence it is possible to employ lubricants which are less prone to generate non-volatile deposits under the action of heat. without reducing the loading on the relatively movable parts which are to be lubricated thereby.

Accordingly, the invention also includes a lubricating composition comprising a major proportion of a lubricant and a minor proportion of the additive as hereinbefore described.

The said lubricant may be of any type, such as hydrocarbon or polyether, but preferably comprises at least one ester, and the ester(s) may be of the so-called hindered type in which there is a quaternary carbon atom either in the alcohol residue(s) beta to the ester linkage(s) and/or in the acid residue(s) alpha to the ester linkage(s).

The ester lubricant may have a viscosity at 210 F. of 7 centistokes or less, for example, between 2 and 6 centistokes, e.g. about 3.3 centistokes. Although the lubricant may have such relatively low viscosities, and correspondingly low load bearing properties (since, generally speaking, for a given type of lubricant, the load bearing properties improve as the viscosity increases), a lubricating composition in accordance with the invention has load bearing properties which are surprisingly high in comparison with the lubricant alone and unexpectedly high in comparison with combinations of the lubricant either with component (a) alone or component (b) alone.

The component (a) may form from 1 to 4 wt. percent of the composition preferably 1.5 to 2.5 wt. percent, while the component (b) may form from 0.025 to 1.0 wt. percent, preferably 0.05 to 0.25 wt. percent of the composition.

A number of lubricating compositions will now be described to illustrate the benefits of the invention.

Two base lubricants of dilfering viscosities but similar chemical constitution were subjected to standard tests to ascertain their load carrying properties.

The base lubricants were (i) Lubricant -A having a viscosity at 210 F. of 5.3 centistokes which is a tetraester of pentaerythritol esterified with a mixture of C -C monocarboxylic acids, and, (ii) Lubricant 13 having a viscosity of 210 F. of 3.3 centistokes and which is a mixture of esters comprising 92 wt. percent of the triester of trimethylol propane esterified with a mixture of approximately C C, monocarboxylic acids and 8 wt. percent neopentyl glycol dipelargonate.

In the tests described hereinafter, both Lubricants A and B were provided with well-known additives to inhibit oxidation of the lubricants and corrosion of metal which the lubricants contact: the concentrations of the oxidation and corrosion inhibitors were approximately the optimum concentrations for their inhibitory action. In addition, a small proportion (0.001 wt. percent) of a known silicone anti-foam agent was included in the lubricants. The lubricants with their oxidation and corrosion inhibitors had approximately the following composition in parts by weight.

3 TABLE I Wt. percent Lubricant A 100.00 Oxidation inhibitor 2.00 Corrosion inhibitor 0.07 Anti-foam agent 0.001 Lubricant B 100.00 Oxidation inhibitor 2.00 Corrosion inhibitor 0.07 Anti-foam agent 0.001

A number of pilot experiments were carried out employing Lubricant A (including its oxidation and corrosion inhibitors) in combination with exemplary embodiments of the components (a) and (b) of the additive of the invention. The chosen exemplary neutral hydrocarbyl phosphate component (a) was cresyl diphenyl phosphate. This is a commercially available compound which is generally prepared by the action of phosphorus oxychloride on a mixture of cresols and phenols.

The chosen exemplary alkylamine hydrocarbyl phosphate component (b) was the easily-made reaction product of a mixture of methyl monoand di-hydrogen phosphates with a commercially available alkylamine product known as Primene 81-R" which is, on average, a C tertiary aliphatic amine.

The component (b) was made as follows:

3 mols of anhydrous methanol were carefully reacted with one mol of phosphorus pentoxide according to the following scheme:

Any excess methanol was removed from the resulting mixture of acid phosphates by vacuum distillation.

If substantially pure monomethyl dihydrogen phosphate is required, the following more elaborate procedure may be adopted: One mol of trisodium phosphate is reacted with one mol of methyl iodide to give the disodium methyl phosphate in admixture with only a small proportion of the dimethyl sodium phosphate, according to the following scheme:

The reaction product is acidified with hydrochloric acid to give the corresponding methyl substituted acid phosphates, and ether extracted.

If it is required that the final product (b) should be dialkylamine monohydrocarbyl phosphate which is completely free from the dihydrocarbyl alkylamine phosphate, the small proportion of dimethyl hydrogen phosphate can be separated from the dihydrogen methyl phosphate by fractional distillation under reduced pressure. However, preliminary studies showed that the presence of the monoalkylamine derivative did not substantially derogate from the advantages of the additive of the invention, especially when the dialkylamine derivative formed the larger proportion of component (b).

The component (b) was, therefore, obtained from the aforesaid mixture of acid methyl phosphates derived by the first described procedure by neutralisation with Primene 81-R: any water remaining in the product was removed by azeotropic distillation.

In the pilot tests on Lubricant A, and the reaction product from the acid phosphates and Primene 81-R consisted approximately of 60 wt. percent dimethyl tertdodecylamine phosphate with 40 wt. percent methyl di- (tert-dodecylamine) phosphate. :Ihe Lubricant A was tested for load bearing characteristics in a standard Four Ball Machine, such as that described in Gear and Transmission Lubricants, C. J. Boner, Reinhold Publishing Corp., New York, 1964, pp. 222-224, without and with the component (a) and (b); the results are summarized in Table II.

(a) plus 0.1 Weight percent (b).

The improvement in load carrying characteristics provided by the addition of component (a) to the Lubricant A is extremely good as will be seen from a comparison of tests 1 and 2. A comparison of tests 1 and 3 shows that the combination of component (b) with Lubricant A provides a superior effect compared with the combination of Lubricant A and component (a).

Finally, pilot test No. 4 provides a result which is surprisingly good in relation to any of the previous tests, and indicates some sort of interaction or synergism between the various additives bearing in mind that increments in loading between any two tests bear approximately a logarithmic relationship to each other. There is no apparent reason for this synergism, and the unexpected discovery forms the basis of the present invention. Test No. 4 gives a load-bearing result for Lubricant A which suggests that the somewhat poorer load bearing properties of the aforedescribed lower viscosity Lubricant B might be improved to a considerable extent sufiicient to render it suitable for use under loading conditions which previously had been considered too severe.

Some tests to confirm the inference drawn from the pilot tests in Lubricant A were carried out on lubricating compositions based on Lubricant B. The tests were carried out on a standard I-AE gear machine with the lubricant or lubricant composition at C. This machine and procedures for using it are described in the Directorate of Engineering Research and Development (Great Britain) 2487 and 2497 specifications as well as in Institute of Petroleum Method 166/ 60T. The failure loads on the TAB machine bear a simple linear relationship to each other, and the results, which are tabulated in Table III below are the failure loads expressed, as is customary in the art, as a percentage of the failure load of a reference lubricant which is a mixture of esters of C C dicarboxylic acids with C C alcohols having a viscosity at 210 F. of 7.5 cs. (i.e. considerably higher than the viscosity of Lubricant B at 210 F). For the tests summarized in Table III, the chosen component (a) was tricresyl phosphate, which is available commercially and may be made in a manner analogous to that described hereinabove for cresyl diphenyl phosphate.

or synergism takes place between the components of the additive of the invention which leads to a very dramatic improvement in the load carrying properties of the lubricating composition based on Lubricant B. It will be seen that the load carrying properties in test 3 exceed those of the more viscous reference oil by a large margin.

The high temperature stability of the compositions employed in tests 1 and 3 of Table III were investigated by the Rolls-Royce confined heat stability test, in which a number of samples of a given lubricant are disposed in closed stainless steel containers for 192 hours, and each container is maintained at a particular temperature for this time. After 192 hours, the samples are tested to determine the weight of toluene-insoluble material: the proportion of tolueneinsoluble material is considered to be a measure of the amount of non-volatile deposit at the test temperature of each sample and an approximation to the proportion of such deposit under operating conditions. The sample which has a toluene-insoluble content of 0.5 wt. percent is considered significant for this test, and its temperature (the so-called S -temperature) during the test determined. If no sample having 0.5 wt. percent of tolueneinsoluble material is found, a theoretical S -temperature can be determined by interpolation or extrapolation from the toluene-insoluble contents of the actual samples.

The following results were obtained.

TABLE IV Lubricating composition: S -temperature, C.

Lubricant B+2s0 wt. percent (a) 290 Lubricant B+2.0 wt. percent (a) +0.1 wt. percent (b) 315 Thus, the composition of test 3 in accordance with the invention will deposit even less non-volatile material at elevated temperatures than the Lubricant B in combination with component (a).

Although the invention has been described with particular reference to examples of component (a) where the hydrocarbyl groups are either cresyl or phenyl, component (a) may equally be any neutral hydrocarbyl phosphate which is soluble in the base lubricant: the aryl or alkaryl neutral phosphates are particularly preferred although neutral aliphatic phosphates may also be used.

Similarly, in component (b), the hydrocarbyl group may be alkyl, phenyl or aralkyl, preferably alkyl, and with from 1 to 9, preferably 1 to 4, carbon atoms per group.

As previously mentioned, the alkylamine group may have on average 8 to 18 carbon atoms per group, preferably 10 to 14 carbon atoms, and may have a tertiary alkyl radical in each alkylamine group.

What is claimed is:

1. An additive for use in a lubricating composition in load-bearing improving amounts comprising the combination of 50 to 97.5 weight percent of a component (a) which is a neutral hydroca-rbyl phosphate in which all three replaceable hydrogen atoms of the phosphate molecule have been replaced by hydrocarbyl groups, and 2.5 to 50 Weight percent of a component (b) which is a neutral alkylamine hydrocarbyl phosphate salt at least some of which is a monohydrocarbyl di(alkylamine) phosphate, in which the hydrocarbyl group of component (b) has from 1 to 4 carbon atoms.

2. An additive according to claim 1 wherein the alkylamine groups of component (h) each have from 8 to 18 carbon atoms.

3. An additive according to claim 1 wherein at least one of the alkyl radicals of the alkylamine groups is a tertiary alkyl radical.

4. An additive according to claim 1 in which the hydrocarbyl group of the component (b) is aliphatic.

5. An additive according to claim 1 in which component (b) includes a neutral monoalkylamine dihydrocarbyl phosphate.

6. An additive according to claim Sin which the proportion of the monohydrocarbyl dialkylamine phosphate in component (b) exceeds the proportion of monoalkylamine dihydrocarbyl phosphate.

'7. An addtive according to claim 1 in which component (a) forms to 97.5 wt. percent.

8. A lubricating composition comprising a major proportion by weight of a lubricant and a minor proportion by weight of the additive in accordance with claim 1.

9. A composition according to claim 8 in which the lubricant comprises at least one ester.

10. A composition according to claim 9 in which the ester has a quaternary carbon atom either in the alcohol residue(s) beta to the ester linkage(s) or in the acid residue(s) alpha to the ester linkage(s) or at both positions.

11. A composition according to claim 8 in which the lubricant has a viscosity of 5 centistokes or less at 210 F.

12. A composition according to claim 8 in which component (a) forms 1 to 4 wt. percent of the composition.

13. A composition according to claim 12 in which component (a) forms 1.5 to 2.5 wt. percent.

14. A composition according to claim 8 in which component (b) forms 0.025 to 1.0 wt. percent of the composition.

15. A composition according to claim 13 in which component (b) forms from 0.05 to 0.25 wt. percent.

References Cited UNITED STATES PATENTS 2,839,468 6/1958 Stewart et al 252-32.5 3,247,109 4/1966 Benoit 25232.5 X 2,146,584 2/1939 Lipkin 252-49.9 X 2,151,380 3/1939 Flint et a1 252-499 X 3,321,401 5/1967 Ford et a1 252-49.9 X 3,476,685 11/1969 Oberender et a1. 252-49.9 X 3,562,300 2/ 1971 Chao et al. 25256 S DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R. 25 249.9 

